In this issue of design disclosure, the Garmin Nuvi 205 with a retail price of only $ 199 is analyzed. It is the first PND (Personal Navigation Device) in blister packaging that I have seen. What attracted my attention was the rows of Nuvi 205 vacuum-packed on the open shelves of a local electronics hypermarket. The price of PND obviously no longer needs to be placed in a locked glass showcase. Nuvi 205 itself and the way it is sold show that the personal GPS system is gradually becoming a popular commodity.
Garmin is not the first nor the only manufacturer to sell PNDs for less than $ 200. But in terms of its price, Nuvi 205 is quite rich in functions. A 3.5-inch 320 × 240 touch screen is used to display full-color Navteq 2D / 3D map data, which is pre-downloaded into Nuvi 205. In addition to the traffic information and news functions of the FM band served by MSN Direct, Nuvi 205 also has a voice turn-by-turn reminder function. The geo-marked pictures on the Google Photo Community Panaramio can be downloaded to the user's MicroSD expansion card, thus providing a more realistic visual experience than the map.
Nuvi 205 even includes car chargers and accessories for fixing on the windshield, so when you buy Nuvi 205, you can get a fairly complete navigation experience without spending more money.
Since Nuvi 205 is aimed at entry-level users, its peripheral interface is quite simple. Nuvi 205's white plastic case has only one "on", "off", and "lock" three-gear slide switch. There is a USB port on the back of the case and a MicroSD expansion card slot on the side. The reset button is hidden in the molded button to prevent abnormal system operation due to locking. It seems that something will never go out of fashion.
Unscrew the two screws hidden under the product label, and open the upper and lower buckle shells, you will see the PCB board that contains all the electronic parts of the system. The LCD touch screen module connected to the PCB is a ZIF slot, and the LCD touch screen is fixed to the upper half of the cabinet by friction fitting. Three screws fix the PCB and the lower part of the chassis together. Once these three screws are removed, you will see the 3.7V / 1250mAh lithium-ion battery and 8Ω speaker under the PCB. Both the speaker and the battery are connected to the PCB using separate wires. Garmin said the battery life and charging time are 4 hours.
The circuit board uses 8-layer drilled glass epoxy PCB technology, which implements all GPS receiver and processor functions. By carefully placing the device to optimize the signal flow, and carefully configuring the pad spacing of the components to achieve the bypass routing through traditional drilling through holes (escape rouTIng), thereby saving the additional cost of high-density PCB technology. When the low price point needs to be considered, every penny must be carefully calculated. At this time, a slight reduction in the cost of raw materials will be crucial.
Garmin uses highly integrated chips to reduce costs. In terms of architecture, the design of Nuvi 205 is only divided into three parts: GPS processing, memory, and analog functions.
In basic GPS processing, ST's single-chip RF front end STA5620 demodulates and converts RF signals from an internal 25mm2 ceramic block patch antenna. Because the independent GPS is less restricted in form than the GPS embedded in other systems (such as mobile phones), a larger antenna with a higher gain than a small stamped metal antenna is still installed in the product . In order to obtain a faster signal positioning time, the American chip LNA is used in the front of the receiver chip to further improve the signal-to-noise ratio.
The signal from the RF receiver is sent to the system, which is responsible for processing the functions of the GPS correlator, system control and peripheral support-a processor marked Garmin-ST. This Garmin-marked processor and ST's "Cartesio" series STA2062 processor based on ARM core and built-in GPS function have many similarities in physical characteristics and functional attributes. It is obviously logical to use it with ST's RF front end. Speech synthesis, LCD control, microcontroller functions, USB and memory interfaces are all just right included.
The system memory used by the processor is 32MB DDR SDRAM from Hynix (memory for work) and SanDisk's 2GB iNAND flash memory. Flash memory is used to store all map data and system code (downloaded to DDR SDRAM) and has a NAND controller that manages the interface with the main processor. Wear leveling or error correction and SD or SPI bus interface formatting are also completed by the controller chip, which is packaged with memory that obviously uses a multi-level cell (MLC) NAND chip.
Simulation function
In addition to GPS and memory, the rest of the system implements the simulation function of the system. Linear Technology's LTC35571 is responsible for USB battery charging and DC-DC conversion; Linear Technology's other chip LT3591 is used for power management of the white LED backlight used by Sharp LCD touch screen modules. The touch screen controller uses TI's TSC2046. TI's other two chips, PCM1774 and TPA2010, respectively implement stereo DAC and audio power amplifier functions.
Each breakthrough in GPS performance and price will trigger a new wave of purchases, and Garmin appears to be intending to attract users who are more price sensitive. With fully functional PNDs appearing in hypermarkets in bulk below $ 200, the next question for Garmin and all its competitors is obviously: How far is it from $ 100?
Figure: Garmin Nuvi 205 internal structure and related components.
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